Kinetic Theory
Category:Physics Lessons First Law of Thermodynamics 1. NJ standards addressed in the unit STANDARD 5.1 (Scientific Processes) All students will develop problem-solving, decision-making and inquiry skills, reflected by formulating usable questions and hypotheses, planning experiments, conducting systematic observations, interpreting and analyzing data, drawing conclusions, and communicating results. Strands and Cumulative Progress Indicators A. Habits of Mind #1 When making decisions, evaluate conclusions, weigh evidence, and recognize that arguments may not have equal merit. #2 Assess the risks and benefits associated with alternative solutions. #3 Engage in collaboration, peer review, and accurate reporting of findings. #4 Explore cases that demonstrate the interdisciplinary nature of the scientific enterprise. B. Inquiry and Problem Solving #1 Select and use appropriate instrumentation to design and conduct investigations. #2 Show that experimental results can lead to new questions and further investigations. STANDARD 5.3 (Mathematical Applications) All students will integrate mathematics as a tool for problem-solving in science, and as a means of expressing and/or modeling scientific theories. A. Numerical Operations #1 Reinforce indicators from previous grade level. B. Geometry and Measurement #1 When performing mathematical operations with measured quantities, express answers to reflect the degree of precision and accuracy of the input data. C. Patterns and Algebra #1 Apply mathematical models that describe physical phenomena to predict real world events. D. Data Analysis and Probability #1 Construct and interpret graphs of data to represent inverse and non-linear relationships, and statistical distributions. STANDARD 5.6 (Chemistry) All students will gain an understanding of the structure and behavior of matter. B. Chemical Reactions #1 Explain that the rate of reactions among atoms and molecules depends on how often they encounter one another and that the rate is affected by nature of reactants, concentration, pressure, temperature, and the presence of a catalyst. #2 Show that some changes in chemical bonds require a net input or net release of energy. STANDARD 5.7 (Physics) All students will gain an understanding of natural laws as they apply to motion, forces, and energy transformations. B. Energy Transformations #1 Explain how the various forms of energy (heat, electricity, sound, light) move through materials and identify the factors that affect that movement. #2 Explain that while energy can be transformed from one form to another, the total energy of a closed system is constant. 2. Length total (days and periods) Total: 11 45 minute class periods (including one test review session) 1-2 90 minute lab periods 1 90 minute test period 3. Prerequisite Prerequisite Knowledge * Knowledge of work and energy, and the work-energy theorem * Knowledge of gases – ideal gas law and their macroscopic and microscopic behaviors 4. Goals Conceptual Conceptual • Understand and distinguish between the concepts of heating and thermal energy • Understand and distinguish between concepts of thermal energy and temperature • Learn to reason qualitatively about thermodynamic processes • Understand and distinguish between concepts of heating and work • Understand and distinguish between reversible and irreversible processes Quantitative *Learn to use the first law of thermodynamics quantitatively in problem solving *Develop relationships for the work done on or by a gas *Develop a relationship between temperature change of a system and the change in internal energy of a system *Develop a relationship between the latent heat of fusion and change in internal energy of a system Procedural * Learn to reason about the first law of thermodynamics processes microscopically and macroscopically * Learn to represent the first law of thermodynamics processes by using words, sketches, bar charts, graphs, and mathematics * Learn to apply these ideas to everyday processes * Learn to represent cyclic systems with energy transfer diagrams and PV, VT, PT diagrams Epistemological * Learn that new concepts are related to previously learned concept * Understand how the processes discussed in the unit are related to real life experiences 5. Key Concepts and Cross-Curricula Links Relationships to Other Units Concepts in thermodynamics relate to previously learned concepts in the following units: * Mechanics * Work and Energy * Gases Most Important Subject Matter Ideas * Recognizing that heating and work are energy transfer processes * There is no such thing as “heat”, but a process called “heating” * Temperature describes the average motion of the molecules in a system * Temperature change is related to the changing energy of a system * The first law of thermodynamics deals with energy conservation of a system 6. Potential Difficulties Student Difficulties * students may have difficulties understanding the differences between heating, thermal energy, and temperature. * understanding adiabatic processes where q=0 but the change in temperature does not equal 0, because students associate temperature with heat * students have difficulty with heat engines, and understanding what a heat engine must be a cyclic process, why the engine requires heat input and output, why Wcycle is equal to the area inside a closed PV curve, and why the change in internal energy is equal to zero * students have difficulty with the different thermodynamic processes and parameters, and also the different relationships between the parameters * it is difficult for students to understand the process shown in a PV graph whether work is being done on or by the system or whether energy is being added or removed from the system 7. Relevance Relevance to Student Lives * thermal equilibrium – when you put any type of drink into a glass with ice – the ice is melted as the drink and the glass cool down. The ice’s increase in temperature and the cooling of the drink and the glass occur because the substances are reaching thermal equilibrium * when students rub their hands together to feel warmer – this involves the thermal energy of your skin molecules being increased, thus increasing the temperature. 8. Curriculum Materials Texts and Materials * The Physics Active Learning Guide Alan Van Heuvelen, Eugenia Etkina * Physics: A General Introduction Alan Van Heuvelen * Online videos ** http://paer.rutgers.edu/pt3 ** ActivPhysics ** http://wps.aw.com/aw_young_physics_11 * PhET ** http://phet.colorado.edu/new/simulations/index.php 9. Full Two Period Lab Thermodynamics Lab LEARNING GOALS OF THIS LAB: # Learn to evaluate how assumptions and uncertainties affect the value of a physical quantity to be determined and to choose experimental procedures least affected by assumptions and uncertainties. # Learn to judge if a physical quantity determined by two different experimental methods are the same or different. I. Application experiment: Specific heat of unknown object Design two independent experiments to determine the specific heat of the given object. The material of which the object is made is not known. Experiment Equipment: You have access to the following equipment: water, ice, container for water, hot plate, Styrofoam container with a cover or a calorimeter, weighing balance, and a digital (!) thermometer. a) First, recall (you don’t have to write anything!) why it is important to design two experiments to determine a quantity. b) Play with the equipment to find how you can use it to achieve the goal of the experiment. Devise as many designs as possible. Write brief outlines for each design. Working with your lab partners, choose the best two designs. Indicate the criteria that you used to decide which designs were the “best”. Show it to your lab instructor. For each method, write the following in your lab-report: (Note: Try to reduce the amount of writing you have to do by referring to earlier points. For example: If some of your assumptions are the same for both methods, just write “see method 1 assumptions”.) c) Write a verbal description and draw a labeled sketch of the design you chose. Include the quantities you will measure. d) Construct the mathematical procedure you will use. e) List all assumptions you make in your design. Decide which of the assumptions affects your results most. Explain how the outcome of the experiment depends on this assumption, i.e. if the assumption increases or decreases your result. f) Design an additional experiment to determine whether the main assumption is valid in your experiment. Quantitatively estimate the effect of this assumption on the value of your measurement and compare it with the instrumental uncertainty (what will happen to your measurements if the assumption is not valid). g) List sources of experimental uncertainty. Decide which is the largest source of uncertainty. Use the weakest link rule to estimate the uncertainty in your result. How would you minimize uncertainties? h) Perform the experiment. Make sure you take steps to minimize experimental uncertainties and the effect of the assumptions. Record your measurements in an appropriate format. i) Calculate the specific heat, based on your procedure and measurements. Include the experimental uncertainty in each value of specific heat that you determine. j) After you have done both experiments, compare the two outcomes. Discuss if they are within your experimental uncertainty of each other. If not, specifically explain what might have gone wrong – perhaps one of your assumptions was not valid. If your experiments are not close to each other within experimental uncertainty, perform the experiment again taking steps to improve your design. For example, you could take all measurements quickly so that hot objects do not cool off, or you could improve the thermal insulation of your calorimeter. II. Why did we do this lab? a) Discuss in your group how a particular value of the specific heat of water might have contributed to the evolution of life on Earth. b) Think of the situation when assumptions such as no friction, no air resistance, no thermal energy loss etc. are not valid. 10. Traditional and Alternative Summative Assessments Traditional Assessment Final Summative Assessment Thermodynamics Test # Your 300 ml cup of coffee is too hot to drink when served at 90.0 °C. What is the mass of an ice cube, taken from a -15.0 °C freezer that will cool your coffee to a pleasant 59.0 °C? # An experiment measures the temperature of a 180 g substance while it is held in an open flame. The figure below shows the results of the experiment. What are (a) the specific heat of the liquid phase and (b) the heat of vaporization? # The average speed of molecules in 1.10 g of hydrogen gas is 703 m/s. A. What is the total microscopic translational kinetic energy of the gas? B. The gas is heated and the internal energy of the system increases by 510 J, causing it to expand and do 210 J of work. Afterwards, what is the average molecular speed? 4. 5.80 g of nitrogen gas at 19.0 °C and an initial pressure of 3.0 atm undergo an isobaric expansion until the volume has tripled. A. How much energy is transferred to the gas to cause this expansion? B. The gas pressure is then decreased at constant volume until the original temperature is reached. What is the gas pressure after the decrease? C.What amount of energy is transferred from the gas as its pressure decreases? 5. For A-D: Starting from equilibrium at point 0, what point on the pV diagram will describe the ideal gas after the following process? A. Lock the piston head in place, and hold the container above a very hot flame. B. Immerse the container into a large water bath at the same temperature, and very slowly push the piston head further into the container. C. Lock the piston head in place and plunge the piston into water that is colder than the gas. D. Wrap the piston in insulation. Pull the piston head further out of the container. 6. Let 1 –kg of liquid water be converted to steam by boiling at standard atmospheric pressure. (see figure 1) The volume changes from an initial value of 1.00 x 10-3 m3 as a liquid to 1.671 m3 as steam. a. How much work is done by the system during this process? b. How much energy must be transferred to the system during the process? c. What is the change in the internal energy of the system during the boiling process? d. Use your results to construct an energy bar chart. Figure 1 7. 0.180 mol of a monatomic gas follows the process shown in the figure below: A. How much heat energy is transferred to or from the gas during process 1 → 2? B. How much heat energy is transferred to or from the gas during process? 2→ 3 C. What is the total change in thermal energy of the gas? 8. The figure below shows a thermodynamic process followed by 2.10×10−2 mol of hydrogen. (a) How much work is done on the gas? (b) By how much does the internal energy of the gas change? © How much energy is transferred to the gas? 9. If you drink cold water, it will soon warm to your body temperature (about 37°C). The water acquires thermal energy from your body. Therefore, you ought to be able to control your weight by drinking lots of cold water. Estimate the volume of cold water you would need to drink so that the energy used to warm it equals the energy released while metabolizing a 240-kcal cinnamon raison bagel. Indicate any assumptions you made. 10. Design and implement a process that will decrease the pressure in the gas cylinder of the figure below without changing the volume. Describe the steps, and then show the process on a pV –diagram and an energy bar chart. Alternative Summative Assessment Alternative Assessment I want to encourage everyone to try something a little different with this chapter. You may opt to complete alternative assignments instead of the test. Below are six options -- choose any 4 to submit for a grade on this chapter. #1 Build a thermocouple and demonstrate it to the class. Your presentation must include a labeled drawing (your own, not downloaded) and a description of how the thermocouple works. #2 We know about the Fahrenheit and Celsius scales. This chapter added the Kelvin scale. Have any other temperature scales been used? What are they, who invented them, when were they invented? The format of this presentation is up to you (a report, poster, slide show, etc.). #3 The word "heat" can be a source of great confusion. When used as a verb, it causes little trouble because it is usually used in an everyday way. For example, you might heat your food in a microwave oven. When used as a now, however, "heat" suggests that there is some substance called heat that, when added to matter, increases its temperature. Collect 5 sentences from newspapers, magazines, and books that use the word both correctly and incorrectly. #4How are the climate and weather affected by adjacent bodies of water? #5 What is the zeroth law of thermodynamics? Explain why it's logically necessary to have this law. Lab website: http://www.ncsu.edu/kenanfellows/2001/plovin/labs/firstlaw.htm Student Projects Out of Classroom Activities 11. Modifications for Different Learners 12. Equipment List and Resources 13. Resource References 14. Reflection on Unit Implementation